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Originally Posted by Eros
1 Paradox concerning Quantum mechanics involiving the decay of a particle.
a stationary spinless particle decays into two others with equal mass (the daughters have equal mass) that are traveling in opposite directions at the velocity of light. Now thats the conservation laws covered... except that of spin.
in the later frame the total spin must be zero.... BUT by quantum mechanics Spin is a property that does not exist untill you try to measure it. (this is comming from lecture notes and not thin air before you lot try and flame me)
SO... if you measure the spin of one of the particles and it is spin up, then at that point in time the other particle (which is two times the speed of light multiplyed by time away) instantly takes spin down to create a system of spin zero.
It is known as the Teleportation Paradox.
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Yes, you are right. This is the standard version of quantum theory that is in most textbooks.
I'd just add that more recent developments suggest that the spins seemingly matching instantaneously when one particle is measured is actually just the result of using a mathematical shortcut called "wave function collapse" and this is not a physical effect, and that the spins match from the moment of the initial split.
[There are technical issues here that I'd rather not get into right now about particles not possessing x and z spins simultaneously.]
The standard textbook version works fine and gives the exact same results, though, despite its slight hiccups with special relativity if the spins matching instantaneously is interpreted as a physical effect.
